Inorganic structural sheet material



United States Patent monoposto STRUCTURAL sanar MATERIAL Lawrence P. Biefeld, Granville, and Marshall C. Armstrong, Hebron, Ghia, assignors to Givens-Corning Fiberglas Corporation, Toledo, Ohio, a corporation of Delaware No Drawing. Application April 17, 1951, Serial No. 221,511

10 Claims. (Cl. 154-86) This invention relates to the fabrication of structural products in the form of panels, boards or molded products with inorganic cements, such as magnesium oxysulpliate or magnesium oxychloride and glass iiber reinforcement. t relates more particularly to the manufacture of a exible, high strength, substantially void-free, low cost structural panel formed of readily available inorganic materials and it is an object of this invention to produce and to provide a method for producing products of the type described.

Another object is to produce and to provide a method for producing a panel of high strength formed of inorganic cenieiits of the type magnesium oXySulphate reinforced and iiexibilized by glass fibers and it is a related object to produce a material or" the type described which is characterized by substantial freedom of voids, high heat resistance and the like such that it can be used for lath, insulation, wall board or table tops.

To make use of glass fibers as a high strength and inert reinforcement in molded or structural products, the industry has had to rely on the use of organic resinous substances and plastics as the bonding agent or base in which the iibers are disposed to form a composite mass. Because of the temperature limitation imposed by the resinous component and the diiiiculty experienced in developing a suitable bonding relation between resinous materials and glass iibers, especially under high humidity conditions, appication of such compositions are limited. The use of inorganic materials as the binder in structural panels or boards has met with considerable discouragement because of the brittle character of the cured cement coupled with their apparent low strength.

it has been found that a material of construction of the type described characterized by high strength, iiexibility in thin sections, nailability and formability may be formed of low cost and readily available inorganic materials base upon the use of glass bers in combination with magnesium oxysulphate cement preferably modied with mineral aggregates such as sand, silica, slate, milled glass and the like and in Which glass iibers function uniquely to impart strength and exibility to the normally iniiexible and brittle cementitious composition.

ln practice, the desired results are obtained when the magnesium oxy'sulphate cement is formed of magnesium oxide and magnesium sulphate (MgSO4-7H2O) present in the ratio of 3-9 mols magnesium oxide to l mol magnesium sulphate with sufiicient Water being present to provide at least ll mols of combined water. Marked improvement is secured when aggregate is present in the ratio of 2 6 parts by Weight aggregate to one of magnesium oxide. The amount of' glass Viiber reinforcement should be in excess of 3 percent by weight of the nal product and it is desirable to introduce as much glass ber as possible, as will hereinafter appear. The amount that can be introduced is limited by the high `viscosity of the slurry formed by the cement and aggregate into which the glass fibers are introduced but 6-10 percent by Weight is usually preferred. Under ordinary conditions as niuch as l5 percent by weight glass fibers may be incorporated and the concentration can be increased by the use or pressure to introduce as much as 27 percent by weight.

Calcined magnesia from various sources, such as from sca water or I. V.tural deposits, may be used but it is preferred to malte use of calcined brucite, such as that derived from the brine at lsuding'ton, Michigan. The latter material is more desirable because the magnesia that is formed exists as rounded particles of relatively uniform size averaging about lil-l2 microns. Magnesia derived from other sources, such as from the Sierra deposit or from sea Water, have much greater variation in particle size ranging from 2-3 microns up to very large particles and, as a result, the latter provides for a much lower bull; density ranging from 30-35 pounds per cubic foot compared to about 5G pounds per cubic foot for calcined brucite. The difference makes possible the preparation of lower viscosity or thinner slurries with equivalent amounts of magnesia so that larger amounts of glass fibers can be incorporated under comparable conditions.

Excellent results have been secured when 1.5-3 parts magnesio. are combined with 3 parts by Weight magn-sium sulphate generally known as Epsom salts. Calculated on the weight basis it is preferred to have the materials present in the ratio of about 2-3 parts magnesia to 3 parts Epsom salts. When mag esiuni sulphate is present in amounts less than 2O percent by weight, the hydrate of magnesia, Mg(OH)2, seem to be produced instead of forming a solid solution with the sulphate and a very weak cement results.

The glass fiber component may be incorporated in various forms. Excellent use may be made of fibers in the form of cut or chopped strands each composed of a hundred or LAlore filaments bundled together, the strands having lengths ranging rom 1/2-4y inches. Less advantageously, use may be made of fibers arranged in fabric form, such as bonded mat of discontinuous fibers or continuous fibers which may be arranged in a swirl pattern, or of continuous iibers in the form of a woven fabric. It is desirable that such bonded or woven fabrics be open sufficient to permit intimate contact with and passage of the binder slurry.

ln the event that the fibers are derived of continuous filaments upon which a size is applied, it is preferred-to make use of a size composition formed of melamineformaldehyde resin, especially when high flexure strength is desired. Excellent use may also be made of a size formed of Water soluble alkyd resins in the forni of a Water soluble condensation product of a polyhydric alcohol with a polybasic acid, or styrene-butadiene copolymer alone or in combination with bentonite or .other clays, or a urea-formaldehyde water soluble resin. Application of the size is made in the usual manner as by wiping onto the filaments as they are drawn from the glass melting bushing and collected into bundles or else application may be made by suitable means after first removing the original size by heat treatment or Washing. ln the event that bonded mat is employed, it is preferred to make use of mat having a minimum amount of organic binder or to make use of bonding agents which are substantially inorganic in character, such as the organo silicon resinous compound.

Suitable aggregate may be selected of eous material, such as sand, int, slate, mica dust, ground glass wool or cullet, chalk, talc and the like. lt is preferred to niale use of fine aggregate of uniform particle size in adinixture with coarse aggregate of substantially uniform size. when such mixture of aggregates are used they should be present in the ratio of 3-5 parts by weight rated therein.

coarse aggregate of about 1Z0-60 mesh to 1-3 parts by weight aggregate in which over 70 percent passes through a 200 mesh screen. It is possibie to achieve the desired results by the use of aggregate in which the particle size is distributed from iine to coarse.

In practice, a slurry is formed of the cement components and aggregate and then the glass fibers are incorpo- TheV amount of fiber and manner of incorporation is limited by the high viscosity characteristic of such cement slurries. In the event that less than 4 percent bers are to be incorporated in the form of cut or chopped strands, they may be combined with the slurry and then cast into molds for forming into intricate shapes or spread upon dat surfaces to form boards or panels. In the event that 4 or more percent glass bers are to be incorporated, the slurry is spread upon a surface, preferably with a separator sheet therebetween and then the glass bers are introduced and integrated into the slurry by means of a spatula, roller or other pressure means. Instead the slurry may be spread in separate thin layers one on top of the other with the glassbers in the form of chopped or cut strands or bonded mat or woven fabrics deposited on top of each layer and preferablyfollowed by a compacting step to integrate the fibers into the layer. When such technique is used for incorporating the glass fibers into the slurry layers, it makes very little difference Whether the fibers are introduced in the form of cut strands, bonded mat, woven fabric or mixtures thereof becauserproper integration can be obtained by subsequent treatment. Up to 20 percent glass fibers may be incorporated by this technique but the amount may be increased to about 80 percent, based upon the final prod- Vuct if the fibers are forced in under high pressure.

' Surface active agents may be used to enhance the wetting out of the aggregate and glass fibers but usage thereof is not essential. The marked improvement in water resistance and weathering which has been claimed from the use of organic acids and salts, such as citric acid, does not seem to take place in compositions embodying the features of this invention but such acids and acid salts may be used.

After the slurry and fibers have been combined and arranged in the molds or sheet form and compressed to the desired thickness, the material may be heated for about 10-60 minutes at temperatures ranging from 15G-200 F. until the cement is cured. After cure, the separator sheets should be peeled off and the product allowed to age for 1-6 days to develop maximum strength. Y

The conditions existing which operate to impart strength and flexibility to an inorganic cement bonded structure of the type described is not capable of explanation at this time. It is apparent, however, that the presence of fine aggregate in admixture and in combination with glass fibers provides for a type of integration which permits sheetshaving a dimension of 1/16 inch or less to be rolled almost as though they were formed of paper whileV the sheet isrfurther characterized by substantial imperviousness, high strength and high heat resistance. These prop- Aerties have heretofore been nnobtainable in inorganic cement compositions. rlhe strength and appearance of the product are improved when the glass iibers are incorporated in the form of swirl or bonded mat with at least two and preferably three or more plies being Kemployed so that at least one can be positioned adjacent each face of the board that is formed to impart a type of Vintegrity and reinforcement which holds the panel together Y follow the batch principle described or may be adjusted to continuous operation wherein the slurry is spread in a thin layer on'a continuous moving belt and the glass fibers later incorporated therein in the form of discontinuous fibers or webs and pressed into the slurry layer by a squeeze roll 0r the like. posited to build up the desired thickness of material and after the desired number of layers have been provided, the mass may be compacted by a series of rollers as the belt passes therebetween and into an air circulating oven maintained at a temperature of about ISO-200 F. for

cure.

' The following examples illustrate the practice of this invention:

Example 1 The magnesium sulphateris dissolved in the water and placed ina mixer. Magnesia is slowly added and allowed to wet out before mixing is started. Whilermixing,l

the aggregateis added and stirring is continued for abou 10 minutes. t

Alternate layers of slurry and 0.6 ounce mat formed of discontinuous strands bonded with phenol formaldehyde resin are spread upon a polyvinyl chloride separator sheet. After the desired number of layers have been deposited and each layer compacted with a suitable roller, another separator sheet is placed on top. In spreading the slurry on with a trowel or the like, care should be taken vto minimize retention of air bubbles to as to produce a substantially void-free product. Three plies of bonded glass mat were sandwiched in this manner between four-layers of slurry and the Ymass further integrated by compression between squeeze rolls or platens to a thickness of about s inch.

The form sheet was then heated in an air circulating oven for 20 minutes at 170 P. and then allowed to cool to room conditions to harden the cement and enable stripping of the separator sheets therefrom. 'Thereafter the material is aged for about 24 hours to 6 days at room conditions to develop optimum properties.

A structure of the type produced by this example has a density of about 110 pounds per cubic footand iiexure strength of 5500 pounds per square inch. In the falling ball impact test, the panel is able to withstand 9 drops from 9 feet; it can be nailed and suitable nailing can be effected 1A inch from the edge. The board is nonammable and can be sheared or cut to desired shapes with an abrasive Wheel.

Y Example 2 Cement formulation:

1 part by weight magnesium oxide (6 mols) 1 part by weight magnesium sulphate (1 mol) 1 part by weight silex sand (95 percent through 200 mesh) 3 parts by Weight sand (30-60 mesh) 1.5 parts by Weight water Cement formulation:

1 part by weight magnesium oxide (4 mols) 1.5 parts by Weight magnesium sulphate (l mol) 1 part by Weight silex sand (95 percent through 200 mesh) Y 3 parts by weight sand (30-60 mesh) 1.5 parts by weight water Successive layers may be de- Example 4 Cement formulation:

1 part by weight magnesium oxide (3 mols) 2 parts by weight magnesium sulphate (1 mol) 1 part by weight silex sand (95 percent through 200 mesh) 3 parts by weight sand (30-60 mesh) 2 parts by weight water The cement compositions of Examples 2-4 inclusive are combined in the manner described in Example 1 to form a slurry and then a layer of the slurry is spread upon a separator sheet formed of highly waxed paper. Three percent by weight of glass fiber strands sized with butadiene-styrene copolymer and cut to 1 inch lengths are rained down from above to form a layer on the slurry which is then incorporated therein. The glass bers may be forced into the slurry by a compacting roller or by spatula and then additional amounts of slurry spread on top to insure complete integration. The deposited mass may be compacted to desired thickness of about G-Ms inch and then heated in an air circulating oven to a temperature of about 170 F. for about 20-30 minutes.

Although the desired results are secured with each of the formulations set forth in Examples 2-4 inclusive, best results were secured with cement compositions in which magnesium oxide and magnesium sulphate is present in the ratio of 4 to 1 on a molecular weight basis, as shown in Example 5.

Example 5 Cement formulation:

l part by weight magnesia 1.5 parts by weight magnesium sulphate 2 parts by weight potters int 3 parts by weight sand (30-60 mesh) 1.5 parts by weight water The slurry was prepared as in Example 1.

Continuous strands of glass fibers sized with butadienestyrene copolymer and cut to 21/2 inch lengths were rained down from above and incorporated by pressing into successive layers of slurry spread on a highly waxed metal plate, The bers were added in amounts to provide 3 percent by weight of the iinal product and the mass compacted to about Ms inch thickness. The mass was then cured as set forth in Example 1 to provide a composite board. The board exhibited a exure strength of about 5500 pounds per square inch and upon impact by the falling ball method gave merely a local fracture on the ninth drop from 9 feet. This is to be compared to the shattering of a panel of Flexboard at the seventh drop from 7 feet. Nails can be placed within 1A: inch of the edges and the panel has very good nailability.

Example 6 Cement formulation:

2 parts by weight calcined brucite 4 parts by weight silex 6 parts by weight milled glass wool 3 parts by weight magnesium sulphate 3 parts by weight water The slurry was prepared as in Example 1.

The slurry was then spread in successive layers on a separator sheet of polyvinylidene chloride, An open mesh fabric of woven glass fibers was deposited on the "rst and next to the last layers and chopped glass bers having fiber lengths distributed between 1/z-3 inches were rained down from above onto each of the layers of slurry in between. The bers in the woven fabric. and in the chopped strands were sized with melamine-formaldehyde resin and they were added in amounts Ato introduce 6-8 percent by weight glass fibers in the iinal product. The deposited layers were compacted by a roller following each deposition of glass bers to compact the layers and to cause more intimate contact between the glass fibers and the slurry. After all of the layers have been so deposited, another separator sheet is placed thereon and the mass further compacted to about 1/a inch thickness. Cure is eifected at a temperature of 150 for 30 minutes and then the mass is allowed to cool at room conditions and then aged for about 6 days.

The concepts of this invention may also be practiced with magnesium oxychloride cements. With magnesium oxychloride, improved results are secured by the use of regate in the cement slurry in substantially the same proportion as employed with magnesium oxysulphate cement but best results are secured when the ratio of coarse and line aggregate is about 1.5 to 1. Glass fibers ranging in amounts from 3-20 percent may be readily incorporated and further amounts up to 30 percent can be introduced by the use of pressure. The following will il strate the practice of this invention with magnesium Oxy/chloride cements.

Example 7 i part by weight magnesium oxide, l part by weight silex (95 percent through 200 mesh), 1-5 parts by weight sand (20-30 mesh), may be combined and gauged to mortar consistency with 22 Baume magnesium chloride solution, 3 percent glass fibers in the form of strands sized with alkyd resin and cut to 1 inch lengths may be incorporated in the manner of fabrication described for magnesiurn oxysulphate. After compacting, the mass may be allowed to cure at room temperature but it is preferred to effect cure by raising the temperature gradually to about 110 F. Thereafter the panel should be further aged at about 50 percent relative humidity.

Flexure strength of boards formed to 1A; inch thiol:- nesses range from 2200-3200 pounds per square inch and they have a modulus of elasticity ranging from .3.S-6.1l l06 pounds per square inch.

Example 8 l part by weight calcined brucite 2 parts by weight potters tlint 0.5 parts by weight coarsely milled glass wool The combined materials are gauged to mortar consistency with a 18-32c Baume solution of magnesium chloride but preferably with a 22 Baume solution. Glass mat in the form of swirl mat formed of continuous fibers dropped in a swirl pattern and bonded with a polystyrene resin or picker mat formed of discontinuous glass fibers dropped in a heterogeneous arrangement and bonded with 2-3 percent phenol formaldehyde resin are incorporated as two or more separate layers into layers of the slurry spread on top of a separator sheet. Compacting should follow deposition of each glass liber layer to eliminate bubbles and insure intimate contact. Cure is effected at a temperature of 90-110 F.

Flexure strength of boards formed by the above process ranges from 1600-2000 pounds per square inch with a modulus of elasticity ranging from 3-SX106 p. s. i. 1mproved results are secured when the milled glass and flint are present in the ratio of 3 to 2.

weathering and water resistance of products embodying features of this invention based upon magnesium oxychloride cement are improved by the addition of citric acid, sodium citrate, other similar organic acids and acid salts, or dimonium phosphate in amounts ranging up to 2 percent by weight. improvement also results when the niagnesia is introduced in finely divided form.

It will be understood that structural panels embodying characteristics of the type described may be prepared without aggregate and that such panels and methods for manufacturing same embody patentable invention and that other changes may be made in the details of fabrication, formulation and selection or" materials based upon the criteria set forth without departing from the spirit of the invention, especially as defined in the following claims.

2. A structural product consisting essentially of curedV magnesium oxysulphate cement based upon components present in the ratioV of 3-6 molecular equivalents magnesium oxide to 1 molecular equivalent magnesium sulphate, siliceous aggregates present in amounts ranging from 2-8 parts by weight per l part by weight magnesium oxide and distributed in the ratio of 3-5 parts by Weight coarse aggregate 26-60 mesh to 1-3 parts by weight tine aggregate having 70 percent passing through 200 mesh, and glass bers in amounts ranging from 3-27 percent by weight `and distributed in the mixture and bonded by the cementy into an integrated composite structure.

3. A structural product as claimed in claim 2 in which -f magnesium oxide is in the form of calcined brucite.

4. A structural product as claimed in claim 2 in which the glass fibers are in the form of bonded mat arranged in separate layers in the final product with at least one layer embeddedV in the cement lying adjacent and substan- .y

tially parallel to each face and in which the materials are formed intoV a sheethaving a thickness of less than IAG inch.

5. Ay structural product as claimed in claim 2 in which Y the glass bers are present in admixture in the form of continuous glass iibers in fabric form and glass fibers in the form of strands cut to shorter lengths.

6. In the method of manufacturing thin exible sheet products with inorganic cements, the steps of forming a slurrywith water suicientto supply the combined water for cure but insufficient to cause free flow and having magnesium oxide and magnesium sulphate present'in the ratio of 3-9 molecular equivalents of magnesium oxide to 1 molecular equivalent magnesium sulphate forV forming magnesium oxysulphate cement incorporating siliceous aggregates into the cement slurry in the ratio of 2-8 parts by weight of aggregate to 1 partby weight of magnesium oxide, spreading the slurry as one or more layers of less than 1/16 inch on a separable mold surface, incorporating glass fibers in the form of open mesh fabric in the slurry layers to position at least one fabric in the slurry adjacent `and parallel to the outer walls of the product and then curing the cement to form the composite product.

7. In the method of manufacturing structural products with inorganic cements, the steps of forming a slurry with Water suflicient to supply the combined water forv cure but insuiicient to cause free ow and with magnesium oxide and magnesium sulphate present in the ratio of 3-6 molecular equivalents of magnesium oxide to 1 molecular equivalent of magnesium sulphate to form a magnesium oxysulphate cement incorporating Vsiliceous aggregates into the slurry in the ratio of 2-8 parts per one part by Weight magnesium oxide, spreading the slurry in one or more successive layers on a mold surface, -incorporating glass fibers in the form of open mesh fabric in an amount ranging from 3-27 percent by weight into the layers, compacting the layers as they are formed to embed the glass bers and insure more intimate contact, and heating the mass to cure the cement and form a composite product. Y

8. The method as claimed in claim 7 in which the siliL ceous aggregate isV divided between fine and coarse aggregate ranging from l-3 parts by weight ne aggregate to 3-5 parts by weight coarse aggregate.

9. The method as claimed in claim 7 in which Vcure is effected by heating the mass to a temperature ranging from 150-200 F, for 10-60 minutes. i

10. In the method of manufacturing structural products with inorganic cements, the steps of forming a slurry with water suflicient to supply the combined water for cure but insucient to cause free ow and having magnesium oxide and magnesium sulphate present in the ratio of 3-9 moiecular equivalents of magnesium oxide to 1 molecular equivalent magnesium sulphate for formingrnagnesium oxysulphate cement, spreading the slurry as one or more layers on a separable mold surface, incorporating glass fibers in the form of open mesh fabric in the slurry layers to position at least one fabric in the' slurry adjacent and parallel to the outerV walls of the product and then curing the cement to form the composite product.

' References Citedin the file of this patent UNITED STATES PATENTS 872,375 Ruet Dec. 3, 1907 909,171 Ellis Ian. 172, 1909 1,853,521 Stewart Apr. 12, i932 2,204,581 Denning June 18, 1940 2,340,209 Sltolnik Jan. 25, 1944 2,405,528 Skolnik Aug. 6, 1946 2,425,883 Jackson Aug. 19, 1947 2,451,445 Parsons Oct. 12, 1948 2,451,446 Parsons Oct. 12, 1948 2,462,538 Nagel Feb. 22, 1949 FOREIGN PATENTS 390,123 Great Britain June 22, 1931 

6. IN THE METHOD OF MANUFACTURING THIN FLEXIBLE SHEET PRODUCTS WITH INORGANIC CEMENTS, THE STEPS OF FORMING A SLURRY WITH WATER SUFFICIENT TO SUPPLY THE COMBINED WATER FOR CURE BUT INSUFFICIENT TO CAUSE FREE FLOW AND HAVING MAGNESIUM OXID AND MAGNESIUM SULPHATE PRESENT IN THE RATION OF 3-9 MOLECULAR EQUIVALENTS OF MAGNESIUM OXIDE TO 1 MOLECULAR EQUIVALENT MAGNESIUM SULPHATE FOR FORMING MAGNESIUM OXYSULPHAET CEMENT INCORPORATING SILICEOUS AGGREGATES INTO THE CEMENT SLURRY IN THE RATIO OF 2-8 PARTS BY WEIGHT OF AGGREGATE TO 1 PART BY WEIGHT OF MAGNESIUM OXIDE, SPREADING THE SLURRY AS ONE ORE MORE LAYERS OF LESS THAN 1/16 INCH ON A SEPARABLE MOLE SURFACE, INCROPORATING GLASS FIBERS IN THE FORM OF OPEN MASH FABRIC IN THE SLURRY LAYERS TO POSITION AT LEAST ONE FABRIC IN THE SLURRY ADJACENT AND PARALLEL TO THE OTHER WALLS OF THE PRODUCT AND THEN CURING THE CEMENT TO FORM THE COMPOSITE PRODUCT. 